Vacuum metallizing of plastic and similar dielectric substance has been practiced for some time. The automobile industry has used metallized trim components that can be substituted for conventional chrome-plated metal parts. The stages of metal film growth by vacuum deposition proceeds from metal nucleation and nuclei growth, liquid coalescence to electrically discrete islands, channelization with incipient film conductivity, and finally fully continuous film formation.
U.S. Pat. No. 4,431,711, issued Feb. 14, 1984 in the name of Eisfeller, assigned to the assignee of the subject invention, discloses one method of vacuum metallizing dielectric substrates with indium and alloys thereof. The patent relates to an article of manufacture comprising organic dielectric bases or substrates having a smooth surface, such as a molded plastic. A macroscopically continuous-appearing very thin layer thereon of indium and alloys thereof, is deposited on the smooth surface. The metal is in the form of minute specular electrically discrete rounded metal islands. There is a top coating over the metal film of an intimately adhered dielectric resin film encapsulating and protecting the metal particles, and binding them firmly to the substrate. The product is particularly useful in automotive applications, such as an automobile exterior trim components to replace heavier and more expensive conventional chrome-plated metal parts.
During the vacuum metallizing process, a vacuum chamber encompasses the dielectric substrate to be coated along with evaporator boats having deposited metal material thereon, which material is evaporated or vaporized onto the substrate. Due to the unique operating characteristics of the vacuum metallizing process, it has been determined that matched evaporation boats, i.e., having similar evaporation rate or heating rates, provides for better part quality and better first run capability. Such is disclosed in U.S. patent application Ser. No. 737,686, filed Jul. 30, 1991, and assigned to the same assignee of the subject invention, now U.S. 5,133,604.
In general, a plurality of evaporation boats are mounted on a horizontal bus bar and connected in parallel or series to a power source during thermal evaporation of the metal material. The evaporation boats are connected horizontally below a rotational carousel which supports the objects to be metallized. The carousel includes a plurality of reels thereon which support the object to be metallized and which may rotate independently of the carousel rotation. The carousel rotates during the evaporation process in order to obtain even adherence of the metal to each object thereon. A problem with this type of system is that indium is generally evaporated only in the vertical direction to mainly horizontal surfaces of the object. Any curved or vertical standing surfaces of the object generally do not receive a coat of the indium, or at least an even coat with relation to the remainder of the object.